Rust compile time port and adapter architecture

This showcase a simple way to define multiple implementations for a single port without involving dynamic dispatch.

Use case

Let say you're building an service, that depends on a database:

• You probably need an in memory implementation of the database for unit testing.
• You may want your service to depend on postgres implementation by default but provide another binary to use with SqlLite.

How

The provided code show a way to achieve this by using conditional compilation and feature flags. The port implementations does nothing more thant setting a boolean and logging.

Building and running with DefaultAdapter :

cargo run

[2023-08-28T13:57:17Z DEBUG rust_compile_time_adapter] Default Adapter done something

Building and running with OtherAdapter :

cargo run --features other_adapter

Running tests:

[2023-08-28T14:01:07Z DEBUG rust_compile_time_adapter] Default Adapter done something
[2023-08-28T14:01:07Z DEBUG rust_compile_time_adapter] Other Adapter done something
[2023-08-28T14:01:07Z DEBUG rust_compile_time_adapter::test] Test Adapter done something

Pros

This allows to use static dispatch to optimize performances and binary size.

It's highly maintainable and simple.

Cons

Mutually exclusives features can be tedious to maintain.

Not the solution if you need to switch adapter at runtime

Remarks

I placed all the code and tests in the main module for convenience. In real application you'll probably want to split modules.